Role of TPN in Control of Glycolysis 233 



1957). 6-PG was determined in a neutralized perchloric 

 filtrate, measuring the height of the plateau obtained after 

 treatment with an excess of TPN and 6-PG dehydrogenase 

 preparation deprived of G-6-P dehydrogenase activity (Glock 

 and McLean, 1953). 



G-6-P and 6-PG dehydrogenases were determined by either 

 one of the two procedures of Glock and McLean (1953). As a 

 measure of hexokinase, the rate of reduction of TPN by 

 glucose plus ATP was considered convenient, provided that 

 the preparation had an excess of G-6-P dehydrogenase. The 

 reduction of DPN, in the presence of fluoride and arsenate, 

 was used to measure some parts of the glycolytic chain, em- 

 ploying different substrates, such as glucose, hexose phos- 

 phates or triose phosphates, according to the purpose of the 

 assay. The detailed composition of the reaction mixtures will 

 be indicated during the presentation of the results. 



Results 



General conditions 



The S2 preparation of rat brain homogenate (supernatant 

 plus microsomes) can convert glucose into lactic acid at a 

 higher rate than the supernatant alone (S3). Notwithstanding, 

 most of the experiments were performed with the latter 

 preparation, which was considered simpler than the former 

 and thus more convenient for our purposes. 



The system does not require that F-di-P be added, as has 

 been done in similar systems by LePage (1948) and by 

 Aisenberg, Reinafarje and Potter (1957). An adequate amount 

 of adenosine triphosphate (ATP) must be provided in the 

 reaction mixture. 



The reaction is markedly d,ependent on the pH of the 

 medium (LePage, 1948), as can be seen in Fig. 1, which also 

 shows the influence of pH on the effect of TPN on glycolysis. 



Effect of mitochondria — The addition of fresh mitochondria 

 decreased glycolysis of brain supernatant, thus confirming 

 previous findings (Aisenberg, Reinafarje and Potter, 1957; 



